Electric cartridge fuse having off-center fusible elements



EMENTS INVENTOR:

ATTORN EY Nov. 26, 1968 F. KozAcKA ELECTRIC CARTRIDGE FUSE HAVINGOFF-CENTER FUSIBLE EL Filed March lO, 1967 United States Patent()3,413,585 ELECTRIC CARTRIDGE FUSE HAVING OFF-CENTER FUSIBLE ELEMENTSFrederick J. Kozacka, South Hampton, N.H., assignor to The Chase-ShawmutCompany, Newburyport, Mass. Filed Mar. 10, 1967, Ser. No. 622,267 4Claims. (Cl. 337-159) ABSTRACT F THE DISCLOSURE A fuse intended topromote heat ow in a direction longitudinally of the fuse tube to keepthe temperature at the center region of the fuse tube relatively low.This end is achieved -by an off-center arrangement of the fusibleelement, or fuse link.

F ielal of invention This invention is concerned with a furtherdevelopment of the current-limiting low volta-ge fuse structuredisclosed and claimed in U.S. Patent 2,939,934 to Frederick I. Kozacka,I une 7, 1960, for Current-Limiting Low Voltage Fuses, assigned to thesame assignee as the present invention. This patent discloses fuseswhose casing or fuse tube is of standard size and whose fuse link orfusible element is of such configuration that its length issubstantially less than that of the casing or fuse tube, the latterbeing made of an inorganic insulating material such as, for instance, asynthetic resin, or a synthetic-resinglass-cloth laminate. Under suchconditions it is nesessary or desirable to limit the highest temperaturewhich may occur :at any point of the casing or fuse tube while the fuseis perfor-ming the current-carrying duty thereof.

Summary of invention The object of limiting the highest temperaturewhich may occur at any point of the casing or fuse tube while the fuseis performing the current-carrying duty thereof is achieved according tothis invention by an arrangement of the fuse link, or fusible element,inside of the casing, or fuse tube, in such a way as to greatly increasethe axial heat flow. To be more specific, the increase of axial heatiiow is achieved by arranging the fuse link otfcenter so that the fuselink is located closer to one end of the fuse tube than to the other endthereof. This, in turn, is achieved by providing a pair of knife bladecontacts of which one is relatively long and the other relatively short,each projecting transversely through one of the terminal caps mounted onthe ends of the fuse tube into the `fuse tube. The relatively long bladecontact has an .axially inner end relatively close to the center regionof the fuse tube and said relatively short blade contact has an axiallyinner end relatively remote from the center region of the fuse tube.

FIG. 2 is a section along 2-2 of FIG. l; and FIG. 3 is a section along3-3 of FIG. 1.

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Description of preferred embodiment The `fuse structure shown in thedrawings is one of standard size whose casing dimensions are determinedby the table below:

The length of the fuse link is substantially less than the standardlength of the fuse tube defined by the table above. The length of thefuse link depends, inter alia, upon the intended voltage rating, thenum-ber of its serially related points of reduced cross-section and thenature of the pulverulent arc-quenching filler. If quartz sand is usedas arc-quenching filler, the number of points of serially related pointsof reduced crosssection may be so high as to limit the length of thefuse link to a substantially shorter distance than twice the safeminimum distance from mid-point of fuse tube to nearest life part asdefined by the U.S. fuse standards. (See Low-Voltage Cartridge Fuses,National Electrical Manufacturers Association Pub. No. FU 1-1963; table35.)

Referring now to the drawings, numeral 1 has been applied to indicate atubular casing of insulating material, preferably a melamine-glassclothlaminate. The ends of casing 1 are closed by caps or ferrules 2, eachhaving an opening for the passage of one of a pair of blade contacts 3.Each blade contact 3 is provided with a transverse bore 4 receiving ahollow radially expandable pin 5. Each of the two pins 5 projectstransversely through coaxial bores provided in casing 1. Pins 6 projecttransversely through caps or ferrules 2 into hollow pins 5, expandingthe latter in radial direction, i.e. increasing the periphery thereof.This establishes a structure of considerable dimensional stability, asmore fully explained in U.S.

Patent 2,939,935 to F. J. Kozacka, June 7, 1960 for Fuse Structures,assigned to the same assignee as the present invention. The axiallyinner ends of blade contacts 3 form .a gap therebetween, and areconductively interconnected by a pair of ribbon fuse links 7. Theaxially outer ends of fuse links 7 sandwich the axially inner ends ofvblade contacts 3. A pair of fuse links 7 is arranged to each side ofblade contacts 3. Each fuse link 7 is provided with three transverselines 7a of perforations, and thus each fuse link 7 has three seriallyrelated points, or areas, of reduced cross-section. The axially outerlines 7a of perforations are sandwiched between plates 9 ofmelamineglass-cloth, and thus separated from the quartz sand filler 8inside of casing 1. The axially inner lines 7a of perforations are notsandwiched in the aforementioned manner between plates ofmelamine-glass-cloth, and thus exposed to the immediate action of thearc-quenching iiller 8 of quartz sand. In this fashion a very desirablecontrol of the arc voltage incident to blowing of the fuse may beachieved. This is explained in considerable detail in U.S. Patent2,964,604 to Philip C. Jacobs et al., Dec. 13, 1960 for Current-LimitingFuses Having Compound Arc-Volt age Generating Means, assigned to thesame assignee as the present invention.

Referring now more particularly to FIGS. 1 and 2, it is apparent thatupper blade contact 3 is considerably shorter than lower blade contact3. The portions of blade contacts 3 projecting beyond the end surfacesof caps or ferrules 2 are equal in length, but the portion of upperblade contact 3 inside of casing l is considerably shorter than theportion of lower blade contact 3 inside of casing 1. As a result, fuselinks 7 whose length is `by far exceeded by that of fuse tube 1 arearranged olf center. In other Words, the axially inner end of the upper,relatively short blade contact 3, to which the upper ends of links 7 areconductively connected, is arranged relatively remote from the centerregion of fuse tube 1, and the axially inner end of the lower,relatively long blade contact 3, is arranged relatively close to thecenter of the fuse tube.

Pins have the same spacing from the ends of fuse tube 1 and a diierentspacing -from the axially inner ends of blade contacts 3. To be morespecific, the spacing of upper pin 5 from the axially inner end of upperblade contact 3 is considerably less than the spacing of lower pin 5from the axially inner end of lower blade contact 3.

It Iwill be understood that though but one embodiment of the inventionhas been illustrated and described in detail, the invention is notlimited thereto. It will also be understood that the structureillustrated may be modilied without departing from the spirit and scopeof the invention as set forth in the .accompanying claims.

I claim as my invention:

1. In an electric low voltage fuse the combination of .a body of quartzsand, a ribbon fuse link having a plurality of serially related pointsof reduced cross-section submersed in said body of quartz sand, a fusetube accomanodating said body of quartz sand and said fuse link, thelength of said fuse tube considerably exceeding the length of said lfuselink, a pair of knife blade contacts conductively interconnected by saidfuse link, one of said pair of blade contacts being relatively long andthe other of said pair of blade contacts being relatively short and eachprojecting transversely through one of said pair of caps into the insideof said casing and into said body of quartz sand, the axially 'inner endof said relatively long blade contact being arranged relatively close tothe center region of said fuse tube and said relatively short bladecontact having an axially inner end .arranged relatively remote fromsaid center region of said fuse tube.

2. An electric fuse as specified in claim 1 wherein said plurality ofpoints of reduced cross-section is suiciently high to limit the lengthof said link to a substantially shorter distance than twice the safeminimum distance from midpoint of the fuse tube to nearest life part.

3. An electric fuse as speciiied in claim `1 wherein the length of saidfuse tube is substantially the length defined by the table below;

and wherein the length of said fuse link is substantially less than thestandard length of said fuse tube as dened by the table above.

4. An electric fuse as specified in claim 1 wherein each of said pair ofblade contacts is supported by a pair of pins each projectingtransversely, through one of said pair of caps and through said fusetube, each of said pair of pins having a spacing of equal magnitude fromthe axially outer ends of said fuse tube and each of said pair of pinshaving a spacing of different magnitude from the axially inner ends ofsaid pair of blade contacts.

References Cited UNITED STATES PATENTS 2,159,423 5/ 1939 Bussmann200--120 XR 2,159,649 5/1939 Alford 200-135 XR 2,281,795 5/ 1942 Pittmanet al. 200-123 XR 3,179,773 4/ 1965 Keeley, Sr. 200--120 3,238,3333/1966 Kozacka 200-120 FOREIGN PATENTS 639,824 7/ 1950 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. HIRAM B. GILSON, AssistantExaminer.

